Method for preventing yarn breakage

ABSTRACT

The invention pertains to the use of a multifilament yarn spinning process comprising individually washing each filament of a multifilament yarn and, if neutralized, individually neutralizing each filament of the multifilament yarn, for preventing yarn breakage during the spinning process, the spinning process comprising spinning of a polymer through a spinneret to obtain the multifilament yarn, washing the yarn, and optionally neutralizing and/or drying the yarn and winding the yarn onto a bobbin Preferably the yarn is washed with jet washers.

The invention pertains to a method for preventing yarn breakage during a spinning process of filament yarn.

It has been a common problem in the manufacture of yarns that the yarns break during liquid processing on roll machines. In liquid processing of yarns, such as in washing yarns immediately after spinning, the yarns are customarily turned several times around pairs of rolls and the yarns are sprayed or otherwise contacted with washing liquids. Process continuity is difficult to maintain due to filament breaks leading yarn breaks and shutdown of the spinning process. It is therefore common to minimize the problem by keeping the spun filaments apart from each other. In U.S. Pat. No. 5,034,250 it was described that yarn breakage during liquid treatment on rolls can be alleviated by using synchronous motors to drive both rolls in a pair. Use of such synchronous motors, set to drive the rolls at substantially the same speed, and taken with the use of rolls having substantially the same diameter, has been found to yield fewer yarn breaks than use of the prior art set up. However, mere use of synchronous roll driving motors does not reduce yarn breakage sufficiently, and slight tension must be applied to the yarns to assure proper advancement and maintenance of proper spacing. To eliminate any attraction between adjacent yarns due to surface tensions of the treatment liquid. It has been recognized that adjacent yarns, when closely-spaced, are pulled even closer together by surface tension forces of the treatment liquid when the liquid can form a liquid web between the yarns. It was further described that the yarns should not be closer than about 0.64 cm from each other to prevent problems. A closer space (also called pitch) leads to filament breakage and wraps and eventual yarn breakage.

This invention relates to a more simple solution of the breakage problem, which allows more freedom regarding the motor drives, and which allows minimizing applied tensions and spacing of the yarns.

It has now been discovered that elimination of filament and yarn breakage can be attained by modifying steps wherein a liquid is applied, such as in washing and neutralization steps. Washing and neutralizing commonly is performed by spraying water over the yarn in a spinning street, or by pulling the spun yarn through a device containing water. Such method is described in U.S. Pat. No. 5,034,250 wherein water is sprayed from a liquid manifold bar to contact the yarns. The yarns are sprayed, and the filaments contained therein are washed as bundle of filaments, but the spray does not individually hit each of the filaments.

In U.S. Pat. No. 5,667,743 a process or wet spinning or aramid fiber has been described. These fibers can be washed in a washing sector using three jet extractor modules. This reference discloses jet washers but it does not disclose that each filament of the yarn bundle is washed individually. This reference further does not disclose the technical teaching that using jet washers can lead to less yarn breakage, provided that the yarn filaments are washed individually.

The inventors have now discovered a novel use of individual washing and neutralizing filaments of multifilament yarn, for example by applying jet washers, in a spinning process for making a multifilament yarn, which use prevents yarn breakage during the spinning process of the multifilament yarn. The spinning process comprises spinning of a polymer through a spinneret to obtain the multifilament yarn, washing the yarn, and optionally neutralizing and/or drying the yarn and winding the yarn onto a bobbin, and is characterized in that each filament of the yarn is individually washed and, if neutralized, is individually neutralized.

It was found that when liquid treatments are performed on the individual filaments of the yarn, particularly with regard to washing and neutralizing treatments, entanglement of the filaments and breakage of the yarn are diminished considerably, even to such extend that synchronous motor drives and precise control of tension and spacing are not longer of utmost importance. It is important to note that the rolls can be rotated at surface speeds having a difference of more than 0.05% under the conditions of this invention, thereby simplifying the spinning and washing/neutralizing process considerably. Use of asynchronous motor drives is also possible under the conditions of this invention and tension control is no longer critical. Spacing which previously should be at least 0.64 cm can easily be diminished to about 0.4 cm, or even to about 0.2 cm without fatal increase of filament entanglement and yarn breakage.

The process of this invention finds particularly use in the washing and neutralizing treatment, or more generally in any liquid treatment of yarns having any denier after spinning the polymer through a spinneret and coagulating the polymer to a yarn and before winding the yarn onto a bobbin. The processing of higher denier yarns benefits the most. Low denier yarns, such as yarns of 70 to 450 dtex, benefit by the less stringent spacing requirements, because low denier yarns are most affected by the surface tension forces of a liquid treatment, are more fragile, and therefore can more easily be damaged.

Liquid treatment of yarns can be conducted at practically any yarn speed ranging from as low as 50 to as high as 1200 meters per minute with yarn breaks occurring at all speeds. The process of this invention permits substantially break-free operation at all speeds for substantially all yarns.

The liquid treatment of the individual filaments can be carried out by any high pressure liquid device that is able to open the yarn bundle to liquid treat single filaments, and is preferably and most easily performed by a multitude of jet washers. Depending on the length of the spin street for instance 5 to 30 jet washers can be used for each yarn. Jet washers are particularly effective in opening yarn bundles and in refreshing the boundary layers that are around each of the filaments. Jet washing of yarn as such is known in the art, for instance from GB 762,959 and WO 93/06266. Jet washers can be used for both the washing and neutralizing treatments, or for other liquid treatments such as applying a coating or finish onto the filaments. Jet washers can be miniaturized, so that for each yarn bundle at least one individual jet washer can be used. A further improvement can be obtained by removing excess water from the yarn. Because adjacent yarns are pulled together by surface tension forces of the treatment liquid, such as water, when the liquid can form a liquid web between the yarns, these attractive forces can be diminished when as few as possible liquid remains on the yarn after washing or neutralizing. It is therefore a further improvement to remove excess liquid from the outer surface of the yarn after having passed the jet washer. Removal of the liquid can be performed by air jets, strippers, pins, and the like.

The process of this invention is particularly useful in washing wet or air gap spun fibers directly after the coagulation bath. Such wet or air gap spun fibers include meta-aramids such as poly(m-phenylene isophthalamide), para-aramids such as poly(p-phenylene terephthalamide) (commercially available as Twaron®, Kevlar®), co-poly-(p-phenylene/3,4′-oxydiphenylene terephthalamide (Technora®), polybenzazole-type fibers such as poly p-phenylene-2-6-benzobis-oxazole (Zylon®), poly{2,6-diimidazo[4,5-b:4′5′-e]pyridinylene-1,4(2,5-dihydroxy)-phenylene} (PIPD, M5®), and the like.

The invention is illustrated by the following examples.

A. Using a conventional roll machine for washing and neutralizing, 440 dtex PPTA (poly(p-phenylene terephthalamide) yarn was treated with water and dilute base. The yarn spacing was 0.48 cm. The spun fiber was washed with water at room temperature using a liquid manifold bar spraying water over the yarn bundles. Run times before breakage were from 4 to 32 hours (average about 15 hours).

B. Using a roll machine for washing and neutralizing 420 dtex PPTA yarn was treated by water and dilute base. The yarn spacing was 0.40 cm. The spun fiber was washed and neutralized using 20 jet washers for each yarn bundle. Run times before breakage were infinitive (run times of months were possible without any breakage). 

1. A method including a multifilament yarn spinning process comprising individually washing each filament of a multifilament yarn and, if neutralized, individually neutralizing each filament of the multifilament yarn, for preventing yarn breakage during the spinning process, the spinning process comprising spinning of a polymer through a spinneret to obtain the multifilament yarn, washing the yarn, and optionally neutralizing and/or drying the yarn and winding the yarn onto a bobbin.
 2. The method according to claim 1 wherein a jet washer is used for washing and neutralizing the yarn.
 3. The method according to claim 2 wherein excess liquid is removed from the outer surface of the yarn after having passed the jet washer.
 4. The method according to claim 1 wherein the multifilament yarn is aramid yarn.
 5. The method according to claim 2 wherein the multifilament yarn is aramid yarn.
 6. The method according to claim 3 wherein the multifilament yarn is aramid yarn. 